Copolymers of carbon monoxide and olefins, such as ethylene, have been known and available in limited quantities for many years. They are usually prepared by reacting the CO and ethylene monomers in the presence of a catalyst. High molecular weight polymers of ethylene which contain small quantities of carbon monoxide can be prepared with the aid of Ziegler catalysts. Low molecular weight polymers of carbon monoxide with ethylene and possibly other olefinically unsaturated hydrocarbons in which all monomer units occur distributed at random within the polymer can be prepared with the aid of radical catalysts such as peroxides. A special class of the copolymers of carbon monoxide with ethylene is formed of the high molecular weight linear copolymers in which the monomer units occur in alternating order in units with the formula --CO--(C.sub.2 H.sub.4)--. Such polymers can be prepared with the aid of, among others, phosphorus-, arsenic-, antimony-, or cyanogen-containing compounds of palladium, cobalt or nickel as catalysts.
The high molecular weight linear alternating polymers of carbon monoxide with ethylene have excellent mechanical properties, in particular very high strength, rigidity and impact-resistance. Due primarily to the high melting point of these polymers, about 257.degree. C., there exist considerable problems in their processing. The processing of these polymers, for example, injection-molding, should take place in a molten state, the material being at a temperature of at least 25.degree. C. above its melting point, i.e. at a temperature of above 280.degree. C. It has been found that these polymers cannot withstand such high temperatures. Serious discoloration and decomposition of the polymers takes place. The high degree of gelling greatly hinders the processing of the polymers.
Attempts have been made in the past to lower the melting point of the polymers through chemical reactions to enable them to be processed at a lower temperature. Examples of such chemical reactions are those in which part of the carbonyl groups present in the polymers are converted into furan-, pyrrol-, thio- or thioketal groups. Although the above-mentioned methods can in a number of cases achieve a considerable reduction of the melting point of the polymers and thus lower the required processing temperature correspondingly, the thermal stability of the polymers is often reduced as a result of the chemical modification to such an extent that the previously mentioned problems such as discoloration, decomposition and gelling occur to practically the same extent, except now at a lower processing temperature.
It should be noted from the above discussion that no solution has yet been found for the problems outlined in processing the polyketones and that there is still an urgent need for a method of lowering the melting point of the polyketone polymers which does not at the same time greatly reduce their thermal stability.
Surprisingly, it has now been found that it is possible to reduce the melting point of the polymers to a value of between 150.degree. and 245.degree. C. without serious detriment to the thermal stability of the polymers by including in the monomer mixture from which the polymers are prepared, in addition to carbon monoxide and ethylene, a relatively small quantity of one or more other polymerizable hydrocarbons. Polymerizable hydrocarbons suitable for this purpose have the general formula C.sub.x H.sub.y in which x is smaller than 20 and contain an olefinically unsaturated --CH.dbd.CH-- group. If a catalyst is employed, such as the previously mentioned palladium, nickel and cobalt compounds enabling a high molecular weight linear alternating polymer to be prepared from a mixture of carbon monoxide and ethylene, the copolymer will consist of units with the formula --CO--(C.sub.2 H.sub.4)--. If the same catalyst is employed and the compound with the general formula C.sub.x H.sub.y is included in the co/ethylene monomer mixture, a terpolymer will be formed containing units with the formula --CO--(C.sub.2 H.sub.4 )-- and different units with the general formula --CO--(C.sub.x H.sub.y)-- distributed randomly within the polymer. The structure of the two polymers differs only in that in the second case a --(C.sub.x H.sub.y)-- group is encountered instead of a --(C.sub.2 H.sub.4)-- group at some random points in the polymer. The surprising result of this structural change is that the melting point is reduced without serious detriment to the thermal stability.
The extent of the melting point reduction depends, among other things, on the value of the quotient m/n, where m represents the mean number of units with the general formula --CO--(C.sub.x H.sub.y)-- and n represents the mean number of units with the formula --CO--(C.sub.2 H.sub.4)-- in the polymer. For polymers of carbon monoxide with ethylene and with a given monomer with the general formula C.sub.x H.sub.y, this dependence means that if n changes, m must change proportionally in order to achieve the same melting point reduction, and that if n is constant, a larger or smaller melting point reduction will be observed as m increases or decreases. In addition, it has been found that the extent of the melting point reduction also depends on the molecular weight of the monomers with the general formula C.sub.x H.sub.y. Finally, the extent of the melting point reduction also depends on the structure of the monomers with the general formula C.sub.x H.sub.y used in the preparation of the terpolymers.